During the past twenty years, vast progress has been achieved in the field of organocatalysis. One of the fruitful areas is iminium catalysis using α, β-unsaturated aldehydes as essential reactants. Enals involved enantioselective reactions (including single-step reactions and cascade/tandem reactions) represent an enormous and fruitful research branch. In contrast, the protocols for the corresponding alkynals, even in single-step conjugate addition reactions, are extremely rare.
Toward this end, my Ph. D. research work mainly focuses on the development of alkynal involved organocatalytic reactions and expands the scope of organocatalysis by uncovering new activation modes. Unlike enals, ynals with sp hybridized C≡C bonds are much less studied and the related chemistries are much less understood. Within the context, firstly, we have developed an organocatalytic regio- and stereoselective Michael additions of 1H-1, 2, 3-triazole to alkynals which afford the trisubstituted alkenes. It is found that the reaction conditions are critical for the 1- vs 2-isomers. Furthermore, we have discovered several novel asymmetric oxa-Michael-Michael/aldol and aza-Michael-aldol(-aromatization) reaction sequences initiated by the Michael addition to alkynals. Notably, an unprecedented chiral iminium-allenamine cascade is disclosed for the first time. Significantly, these processes serve as efficient and straightforward entries to biologically significant chiral 4H-chromenes, polysubstituted quinolines and chiral 1,4-dihydroquinolines with excellent yield and enantioselectivity, as well as broad substrate compatibility. The proposed iminium-allenamine activation mode adds a new domain in the field of organocatalytic enantioselective cascade reactions. Finally, unprecedented organocatalytic 1,6-conjugated addition to yenals, an unmet challenging problem in organic synthesis, also has been realized.